1. Field of the Invention
The present invention relates to a delay profile making method and a delay profile making apparatus.
2. Description of Related Art
A receiver of W-CDMA system determines the arrival timings of paths that enable RAKE combining, and makes delay profiles during the process of establishing synchronization.
As for the process of making a delay profile, commonly, received data that corresponds to a given search period is temporarily stored in a storage memory; when the storing is done, the data is read at an appropriate timing and supplied to an correlation detector (i.e. matched filter) for correlation detection; in-phase addition is performed with respect to the obtained correlation level; and, utilizing this in-phase addition, power calculation is performed to make a delay profile.
Incidentally, the above power calculation that utilizes in-phase addition refers to a method of calculating power by accumulatively adding a number of in-phase data (i.e. having + or − in common) and performing square calculations with respect to the accumulative calculation values, instead of performing a square calculation on a per received data basis and adding the calculation results. The accumulative calculation has the merit of enlarging the number and improving the S/N.
Typically, the pattern of pilot signals and such, which provides the foundation in delay profile making, is a pattern in which simply the same positive or negative data such as “+1” and “−1” continues.
This, consequently, makes it possible to accumulatively add a given number of correlation levels that are output from a matched filter (i.e. correlation detector) on a continuous basis, and perform in-phase addition operations efficiently.
In such case, changing the number of symbols that are subject to in-phase addition is not difficult, and when efficient power calculation is desired, the number of symbols that are subject to in-phase addition needs to be increased.
However, as described in W-CDMA Communication Systems, ed. Keiji Tachikawa, 2nd ed. (Tokyo: Maruzen, 2001), 109–110, the secondary CPICH in the CPICH (Common Pilot Channel), which is a physical layer in W-CDMA system, uses patterns, in which “+1” and “−1” exist in a mixed manner, for pilot symbol patterns.
Consequently, if correlation detection is performed with respect to the secondary CPICH (referring mainly to cases where channel estimation is performed for each path while the adaptive array antenna is in use), as in the conventional case, by simply accumulatively adding the correlation levels, the positive data and the negative data cancel out each other, and the accumulative addition value becomes 0, thereby making it impossible to detect correlation.
Therefore, performing in-phase addition requires ingenuity that divides data on a per pattern basis and that adds the data at the corresponding positions in respective patterns (i.e. data that share the same + and −).
For instance, if the basic pattern is “+1, −1, −1, +1,” it becomes necessary to divide and extract output from a matched filter per four symbols, and add the +1's and the −1's.
However, data processing performed on a per 4-symbol unit basis necessarily increases the number of times of operation and increases the time required for the accumulative addition operation processing. If a method stores all received data from a search period and performs correlation detection as in the conventional case, the processing time before delay profile making becomes long compared to the conventional case, and this becomes an obstacle to timely establishment of synchronization.
Moreover, where the secondary CPICH is used in delay profile making, it is preferable that, before the accumulative addition of four symbols of data (correlation levels) is complete, the following four symbols are output from a matched filter, and furthermore, in view of processing efficiency, it is important that four symbols of data flows in continuously in a pipeline manner, and the conventional art fails to meet these demands.